I plan to add rear fog at the center location which I don't have one right now. I plan to just tap it to the front fog line so I don't have to change the toggle switch. It will just turn on at the same time when I turn the front fogs on.
Question is, will it affect the load on that line or do I have to increase the fuse for that line? or if it were extra back-up light and tapped to the rear line, will it put strain on the load for that line? Thanks in advance for any input.

 

Personally I would be comfortable enough with the amount of additional load that I wouldn't do anything special to handle it. If you want to be cautious, just replace the bulb in the new lamp with a compatible LED bulb, which will draw an almost negligible amount of load.

I have been using the center location as an additional backup light for over 4 years with no issues.

The front fogs are 55 watts EACH, and a rear fog is 21 watts.